Semiconductor wafers such as silicon and gallium arsenide wafers and various types of packages (which may foe collectively referred to as “cut object(s)” herein) are manufactured in a large diameter state, and these are cut and separated (diced) into small element pieces (referred to as “chip(s)” hereinafter).
A cut object to be supplied to the dicing process may be such that, for the purpose of ensuring the handling property of the cut object and chips in the dicing process and subsequent processes, a dicing sheet comprising a base film and a pressure-sensitive adhesive layer provided thereon is preliminarily applied to a surface of the cut object opposite to the side which a cutting tool for cutting comes close to. Such a dicing sheet may typically use polyolefin-based film or polyvinyl chloride-based film as the base film, for example.
According to commonly-used full-cut dicing as a specific method for the dicing process, a rotating round blade is used for cutting a cut object. In the full-cut dicing, to ensure that the cut object applied thereto with the dicing sheet is completely cut over the entire surface, the pressure-sensitive adhesive layer may also be cut beyond the cut object, and a part of the base film may further be cut.
During this operation, dicing debris comprising material that constitutes the pressure-sensitive adhesive layer and the base film may arise from the dicing sheet, and the obtained chips may be contaminated by the dicing debris. One form of such dicing debris is filament-like dicing debris that attaches onto a dicing line or to an area near the cross-section of each chip separated by dicing.
If the chip is enclosed in a package while a large amount of the filament-like dicing debris as described above remains on the chip, then the filament-like dicing debris attached to the chip will be decomposed by heat used for the enclosing, and the thermally decomposed substance may destroy the package and/or cause operational failure in a device to be obtained. Such filament-like dicing debris is difficult to be removed by washing, and the yield of the dicing process will thus be significantly reduced due to the occurrence of filament-like dicing debris. Hence, the filament-like dicing debris may have to be prevented from occurring when dicing is performed by using a dicing sheet.
When dicing a package as the cut object in which plural chips are enclosed by using cured resin, a dicing blade having a thicker blade width is used and the cutting depth in dicing also becomes deeper than the case of dicing a semiconductor wafer. Consequently, the amount of the base film to be cut and removed during the dicing may increase compared with the case of a semiconductor wafer, so that the generated amount of filament-like dicing debris also tends to increase.
To suppress the occurrence of such dicing debris, Patent Literature 1 discloses an invention which uses, as the base film of a dicing sheet, a polyolefin-based film having been exposed to electron beam or γ (gamma) ray with 1-80 Mrad. In this invention, it appears that a resin that constitutes the base film is crosslinked through the exposure to electron bese or γ ray thereby to suppress the dicing debris from being generated.
Patent Literature 1 exemplifies, as materials for the polyolefin-based film to be exposed to electron beam or γ ray, resins such as polyethylene, polypropylene, polymetnylpentene, styrene-vinyl acetate copolymer, ethylene-(meth)acrylic acid copolymer, ethylene-methyl(meth)acrylic acid ester copolymer, ethylene-ethyl(meth)acrylic acid copolymer, ethylene-ionomer copolymer, ethylene-vinyl alcohol copolymer, and polybutene.